In recent years, for a touch panel apparatus with a touch panel being provided on a display unit, a technology called forced feedback that provides tactile feedback from an operation key being pressed to an operator has been proposed (see for example Patent Document 1). In Patent Document 1, a piezoelectric element is provided on the touch panel. In the technology disclosed in Patent Document 1, tactile feedback is provided to an operator by vibrating the touch panel as a result of contractive deformation of the piezoelectric element by applying voltage to the piezoelectric element in response to the operator's touch on an operation face of the touch panel.
A technology that detects a pressing force applied on an operation key by a pressure sensor for selection and execution of a particular function, as well as adjustment and change of properties of functions according to the pressing force thus detected has also been proposed (see for example Patent Document 2). In the technology disclosed in Patent Document 2, an operator is notified of a selected function or properties thereof by means of vibration generated every time the pressing force exceeds a preset threshold.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-175364
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-244789